Microwave dielectric ceramic composition

ABSTRACT

A microwave dielectric ceramic composition which is obtained by selecting, in a composition formula of (A 1+   1/2  ·B 3+   1/2 ) TiO 3 , Li 1+   and Nd 3+ , Co 3+   or Pr 3+   as A 1+  and B 3+ , respectively. The dielectric ceramic composition expressed by (A 1+   1/2  ·B 3+   1/2 ) TiO 3  has a high dielectric constant and has a temperature coefficient of resonance frequency τf which is large on the minus side. MgO, CoO, ZnO, CaCO 3  or SrCO 3  is added to such a dielectric ceramic composition expressed by (A 1+   1/2  ·B 3+   1/2  /TiO 3 , to improve the Q value of the dielectric ceramic composition.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to dielectric ceramic compositions for use as resonators employed in a microwave frequency band of several gigahertz.

2. Description of the Prior Art

In recent years, attempts have been made to use a dielectric material for a resonator or a filter used in satellite communication, broadcasting and microwave remote communication using a microwave a frequency band of several gigahertz. A transmitter-receiver such as a microwave remote recognition system is also sought.

Examples of this type of dielectric ceramic material conventionally used include a composition of a BaO-TiO₂ -Nd₂ O₃ -Bi₂ O₃ system which is proposed in, for example, Japanese Patent Laid-Open Gazette No. 8806/1986. In this conventional dielectric ceramic composition, its dielectric constant ε is as high as 70 to 90. In addition, the temperature coefficient of resonance frequency τf of the dielectric ceramic composition is also high, i.e., +10 to about +20 PPM/°C., so that sufficient properties cannot be obtained.

Meanwhile, when a dielectric resonator is constructed, the higher the dielectric constant ε of a material used, the smaller the size the resonator can be. Accordingly, a material having a higher dielectric constant ε is desired.

Examples of a material having a high dielectric constant ε include SrTiO₃ and CaTiO₃. However, these cannot be used because the dielectric constant ε is very high, i.e., 300 and 180, while their temperature coefficient of resonance frequency τf is very high, i.e., +1700 PPM/°C. and +800 PPM/°C.

Examples of a method of reducing the temperature coefficient of resonance frequency τf of such a dielectric ceramic composition include a method of combining a material having a dielectric constant ε which is as high as possible and a temperature coefficient of resonance frequency τf which takes a minus value with the dielectric ceramic composition. According to this method, a ceramic composition having a high dielectric constant ε and having a low temperature coefficient of resonance frequency τf is obtained by a suitable combination.

In general, however, as the dielectric constant ε becomes higher, the temperature coefficient of resonance frequency τf becomes larger on the plus side. A material having a high dielectric constant ε and a temperature coefficient of resonance frequency τf which is large on the minus side has not been known.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above described points and has for its object to obtain a dielectric ceramic composition having a high dielectric constant ε and having a temperature coefficient of resonance frequency τf which is large on the minus side.

Another object of the present invention is to improve the Q value of such a dielectric ceramic composition.

Still another object of the present invention is to provide a dielectric ceramic composition having a high dielectric constant ε and having a temperature coefficient of resonance frequency τf which is close to zero.

When a microwave dielectric ceramic composition according to the present invention is expressed by a composition formula of (A¹⁺ _(1/2) ·B³⁺ _(1/2)) TiO₃, Li¹⁺ and Nd³⁺, Sm³⁺, Co³⁺ or Pr³⁺ are respectively selected as A¹⁺ and B³⁺.

Furthermore, the present invention provides a dielectric ceramic composition obtained by suitably selecting MgO, CoO, ZnO, CaCO₃ or SrCO₃ and adding the same to the ceramic composition expressed by (A¹⁺ _(1/2) ·B³⁺ _(1/2)) TiO₃.

The above described dielectric ceramic composition expressed by (A¹⁺ _(1/2) ·B³⁺ _(1/2)) TiO₃ has a high dielectric constant ε and has a temperature coefficient of resonance frequency τf which is large on the minus side. MgO, CoO, ZnO, CaCO₃ or SrCO₃ is added to such a dielectric ceramic composition (Li_(1/2) ·B³⁺ _(1/2)) TiO₃, thereby to improve the Q value of the dielectric ceramic composition.

Additionally, when the microwave dielectric ceramic composition according to the present invention is expressed by a composition formula of w·A¹⁺ ₂ O-x·A^(1+') ₂ O-y·B³⁺ ₂ O₃ -z·TiO₂ (where w+x+y+z=100 mole %), Li¹⁺, Na¹⁺, and Nd³⁺ or Sm³⁺ are respectively selected as A¹⁺, A^(1+'), and B³⁺.

As described in the foregoing, a dielectric ceramic composition mainly composed of Li₂ O-Na₂ O-Sm₂ O₃ -TiO₂ and a dielectric ceramic composition mainly composed of Li₂ O-Na_(Na) ₂ O-Nd₂ O₃ -TiO₂ have a high dielectric constant ε and have a low temperature coefficient of resonance frequency τf.

Furthermore, when the microwave dielectric ceramic composition according to the present invention is expressed by a composition formula of v·B^(3+') ₂ O₃ -w·A¹⁺ ₂ O-x·A^(1+') ₂ O-y·B³⁺ ₂ O₃ -z·TiO₂ (where v+w+x+y+z=100 mole %), Li¹⁺, Na¹⁺, Sm³⁺, and Nd³ + or Pr³⁺ are respectively selected as A¹⁺, A^(1+'), B³⁺, and B^(3+').

As described in the foregoing, a dielectric ceramic composition mainly composed of Nd₂ O₃ -Li₂ O-Na₂ O-Sm₂ O₃ -TiO₂ and a dielectric ceramic composition mainly composed of Pr₂ O₃ -Li₂ O-Na₂ O-Sm₂ O₃ -TiO₂ have a high dielectric constant ε and have a low temperature coefficient of resonance frequency τf.

Furthermore, when the microwave dielectric ceramic composition according to the present invention is expressed by a composition formula of w·A¹⁺ ₂ O-x·CaO-y·B³⁺ ₂ O₃ -z·TiOhd 2 (where w+x+y+z=100 mole %), Li¹⁺ and Sm³⁺ or Nd³⁺ are respectively selected as A¹⁺ and B³⁺. Thus, a dielectric ceramic composition mainly composed of Li₂ O-CaO-Sm₂ O₃ -TiO₂ and a dielectric ceramic composition mainly composed of Li₂ O-CaO-Nd₂ O₃ -TiO₂ have a high dielectric constant ε and have a low temperature coefficient of resonance frequency τf.

Additionally, when the microwave dielectric ceramic composition according to the present invention is expressed by a composition formula of x·(Li_(1/2) ·B³⁺ _(1/2)) TiO₃ -(100-x)·CaTiO₃ (Where 0 mole %<x<100 mole %), Nd³⁺ or Sm³⁺ is selected as B³⁺.

Furthermore, when the microwave dielectric ceramic composition according to the present invention is expressed by a composition formula of x·(Li_(1/2) ·B³⁺ _(1/2)) TiO₃ -100-x)·(Na_(1/2) ·C³⁺ _(1/2)) TiO₃ (where 0 mole %<x<100 mole %), Nd³⁺ or Sm³⁺ and Nd³⁺ or Sm³⁺ are respectively selected as B³⁺ and C³⁺.

Moreover, the above described dielectric ceramic composition (Li_(1/2) ·B³⁺ _(1/2)) TiO₃ and a dielectric ceramic composition (Na_(1/2) ·C³⁺ _(1/2)) TiO₃ or CaTiO₃ are combined with each other, thereby to obtain a dielectric ceramic material having a high dielectric constant ε and having a low temperature coefficient of resonance frequency τf.

The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a characteristic diagram showing a characteristic curve of a dielectric constant ε and a temperature coefficient of resonance frequency τf against the mixture ratio of (Li_(1/2) ·Sm_(1/2)) TiO₃ to (Na_(1/2) ·Sm_(1/2)) TiO₃ according to the present invention;

FIG. 2 is a characteristic diagram showing a characteristic curve of a dielectric constant ε and a temperature coefficient of resonance frequency τf against the mixture ratio of (Li_(1/2) ·Nd_(1/2)) TiO₃ to CaTiO₃ according present invention; and

FIG. 3 is a characteristic diagram showing a characteristic curve of a dielectric constant ε and a temperature coefficient of resonance frequency τf against the mixture ratio of (Li_(1/2) ·Sm_(1/2)) TiO₃ to CaTiO₃ according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Description is now made of a first embodiment of the present invention.

A microwave ceramic composition according to the first embodiment is obtained by selecting, in a composition formula of (A¹⁺ _(1/2) ·B³⁺ _(1/2)) TiO₃, Li¹⁺ and Nd³⁺, Sm³⁺, Co³⁺ or Pr³⁺ as A¹⁺ and B³⁺, respectively.

First, a method of fabricating the microwave ceramic composition will be described.

As raw materials, high-purity powders of TiO₂, Li₂ CO₃, Nd₂ O₃, Sm₂ O₃, Co₂ O₃, Pr₆ O₁₁ were weighed so as to be predetermined molar fractions. For example, used as TiO₂ is one of a high-purity grade which is manufactured by Toho Titanium Co., Ltd.; used as Li₂ CO₃ is one of a 3N grade which is manufactured by Kojundo Kagaku Co., Ltd.; used as Nd₂ O₃ is one of a 3N grade which is manufactured by Mitui Mining and Smelting Co., Ltd.; used as Co₂ O₃ is one of a reagent grade which is manufactured by Kojundo Kagaku Co., Ltd.; and used as Pr₆ O₁₁ is one of a 3N grade which is manufactured by Mitui Mining and Smelting Co., Ltd.

Description is made of a specific example of the fabrication of the microwave dielectric ceramic composition according to the present embodiment using the above described raw materials.

First, as molar fractions of the high-purity powders of TiO₂, Li₂ CO₃, Nd₂ O₃, Sm₂ O₃, Co₂ O₃, and Pr₆ O₁₁, TiO₂ shall be 1 mole, Li₂ CO₃ shall be 1/4 mole, Nd₂ O₃ shall be 1/4 mole when Nd₂ O₃ is selected in addition thereto, Sm₂ O₃ shall be 1/4 mole when Sm₂ O₃ is selected in addition thereto, Co₂ O₃ shall be 1/4 mole when Co₂ O₃ is selected in addition thereto, and Pr₆ O₁₁ shall be 1/12 mole when Pr₆ O₁₁ is selected in addition thereto.

The raw material powders, a nylon ball of 15φ and ethyl alcohol were put in a nylon pot, mixed in the following condition, and wet-blended for eight hours.

Raw material powders:Nylon ball:Ethyl alcohol=100 g:500 g:500 cc

The blended powder was then dried at 120° C. for 24 hours. The dried powder was crushed in a mortar made of alumina. The crushed powder was packed in a boat made of magnesia (MgO) and calcined at 900° to 1200° C., and particularly, at 1150° C. in the present embodiment for two hours. The calcined powder is crushed again in the mortar.

This crushed powder was put in the nylon pot under the following condition and wet-ground for 20 to 60 hours, and particularly, for 30 hours, in the present embodiment.

Crushed powder:Nylon ball:Ethyl alcohol=100 g:1000 g:500 cc

Subsequently, this ground powder was dried at 120° C. for 24 hours. The dried ground powder was crushed, and a 10 solution of polyvinyl alcohol is mixed as a binder so as to account for three per cent of 50 g of the powder using the mortar to granulate the powder. The granulated powder was dried at 100° C. for five hours.

Thereafter, the dried powder was classified using two types of screens, that is, a 100-mesh screen (150 μm) and a 200-mesh screen (75 μm), to take out only grains having a diameter of 75 to 150 μm.

The classified powder was pressed into a disc having a diameter of 10 mm and a thickness of 6 mm at a pressure of 2000 to 3000 Kg/cm², and particularly, 2550 Kg/cm², in the present embodiment.

Subsequently, the pressed forming powder was put in a boat for sintering made of alumina with a plate made of zirconia (ZrO₂) being laid on the bottom thereof, and was held and sintered for two hours at 350° C., for two hours at 600° C. and for five hours at 1300° C. at a heating rate of 150° C./H. Both surfaces of the sintered object ware polished using abrasive powder OF-800# manufactured by, for example, Fujimi Abrasive Co., Ltd. such that the thickness of the sintered object is one-half of the diameter thereof. In addition, both surfaces of the polished object were polished clean again using wet abrasive paper 1500#. Thereafter, the polished object was ultrasonic cleaned by acetone and finally, dried at 100° C. for two hours to prepare a sample.

The dielectric constant ε and the Q value of the sample thus prepared were measured using a network analyzer (YHP 8510B) in the neighborhood of the measurement frequency of 3 GHz using the dielectric resonator method (Hakki-Coleman method). In addition, the temperature coefficient of resonance frequency τf was calculated from the following equation by putting a measuring system in a constant temperature bath to measure the change in resonance frequency at 0° to 70° C.: ##EQU1## where F₇₀ denotes a resonance frequency at 70° C., F₂₀ denotes a resonance frequency at 20° C., and ΔT denotes a temperature difference.

The results of measurements made by varying A¹⁺ and B³⁺ are shown in Table 1.

                  TABLE 1                                                          ______________________________________                                         sam-                                                                           ple        dielectric properties                                               num- composition                                                                              dielectric                                                                               Q     τ f                                         ber  A.sup.+1                                                                              B.sup.3+                                                                              constant ε                                                                     value (PPM/°C.)                                                                       note                                  ______________________________________                                         1    Li.sup.1+                                                                             Nd.sup.3+                                                                             80      430   -310                                          2    Li.sup.1+                                                                             Sm.sup.3+                                                                             52      470   -260                                          3    Li.sup.1+                                                                             Co.sup.3+                                                                             31      2200   -58                                          4    Li.sup.1+                                                                             Pr.sup.3+                                                                             92      340   -405                                           5*  Li.sup.1+                                                                             Cr.sup.3+                                                                             --      --    --      impossible                                                                     to measure                             6*  Li.sup.1+                                                                             La.sup.3+                                                                             --      --    --      impossible                                                                     to measure                             7*  K.sup.1+                                                                              Nd.sup.3+                                                                             --      --    --      impossible                                                                     to measure                            ______________________________________                                    

In the table 1, asterisked samples 5 to 7 are comparative examples beyond the scope of the present invention. In a combination in the comparative example, the sample is sintered. However, the sample is inferior in dielectric properties in the microwave region, thereby making it impossible to measure the sample.

On the other hand, as can be seen from the table 1, a ceramic composition having a high dielectric constant ε and having a temperature coefficient of resonance frequency τf which is large on the minus side is obtained by selecting, in a composition formula of (A¹⁺ _(1/2)·B³⁺ _(1/2)) TiO₃, TiO₃, Li¹⁺ and Nd³⁺, Sm³⁺, Co³⁺ or Pr³⁺ as A¹⁺ and B³⁺, respectively.

Description is now made of a second embodiment. A ceramic composition according to the second embodiment is obtained by adding to the ceramic composition (Li_(1/2) ·B³⁺ _(1/2)) TiO₃ obtained in the above described first embodiment MgO, CoO or ZnO when B³⁺ is Nd³⁺ or Pr³⁺ or CaCO₃, SrCO₃ or ZnO when B³⁺ is Sm³⁺. A predetermined part by weight of CaCO₃. SrCO₃ or ZnO is added to 100 parts by weight of main components of (Li_(1/2) ·B³⁺ _(1/2)) TiO₃. As this additive, used as CaCO₃ is one of a reagent grade which is manufactured by Kishida Chemical Co., Ltd., used as SrCO₃ is one of a reagent grade which is manufactured by Kishida Chemical Co., Ltd., or used as ZnO is one of a 3N grade which is manufactured by Kojundo Kagaku Co., Ltd.

In the second embodiment, a predetermined amount of the above described additive is mixed with powder obtained by wet-blending respective raw materials of the main components of (Li_(1/2) ·B³⁺ _(1/2)) TiO₃, followed by dryblending. Thereafter, a sample is completed by calcination, forming and sintering in the same method as that in the first embodiment.

The results of measurements made of the dielectric properties of samples to be measured which are prepared by varying the amount of addition of each of the above described additives in the neighborhood of the measurement frequency of 3 GHz using the Hakki-Coleman method are shown in Table 2, Table 3 and Table 4.

Table 2 shows the results of measurements made when MgO, CoO or ZnO is added to (Li_(1/2) ·Nd³⁺ _(1/2)) TiO₃.

Table 3 shows the results of measurements made when CaCO₃, SrCO₃ or ZnO is added to (Li_(1/2) ·Sm³⁺ _(1/2)) TiO₃.

Table 4 shows the results of measurements made when MgO, CoO or ZnO is added to (Li_(1/2) ·Pr³⁺ _(1/2)) TiO₃.

                  TABLE 2                                                          ______________________________________                                                        dielectric properties                                           sample  additive     dielectric                                                                              Q      τ f                                   number  (part by weight)                                                                            constant ε                                                                      value  (PPM/°C.)                          ______________________________________                                                 MgO                                                                     8      0            80        430   -310                                       9      1            71        900   -207                                      10      3            56       1873   -149                                      11      5            48       1939   -150                                      12      10           40       2023   -194                                              CoO                                                                    13      0            80        430   -310                                      14      1            71        844   -262                                      15      3            64       1318   -173                                      16      5            57       1936   -145                                      17      10           44       3181    -82                                              ZnO                                                                    18      0            80        430   -310                                      19      1            71        841   -275                                      20      3            66       1183   -169                                      21      5            55       2203   -126                                      22      10           42       2841    -27                                      ______________________________________                                    

                  TABLE 3                                                          ______________________________________                                                        dielectric properties                                           sample  additive     dielectric                                                                              Q      τ f                                   number  (part by weight)                                                                            constant ε                                                                      value  (PPM/°C.)                          ______________________________________                                                 CaCo.sub.3                                                             23      0            52        470   -260                                      24      1            56        676   -322                                      25      3            62       1301   -154                                      26      10           49       1073   -275                                       27*    15           58       1680    -38                                              SrCO.sub.3                                                             28      0            52        470   -260                                      29      3            60        833   -272                                      30      5            63        909   -267                                      31      10           55        916   -232                                       32*    15           65        386    -45                                              ZnO                                                                    33      0            52        470   -260                                      34      1            59        752   -230                                      35      3            48       1003   -192                                      36      5            43        767   -110                                       37*    15           35       1196     57                                      ______________________________________                                    

                  TABLE 4                                                          ______________________________________                                                        dielectric properties                                           sample  additive     dielectric                                                                              Q      τ f                                   number  (part by weight)                                                                            constant ε                                                                      value  (PPM/°C.)                          ______________________________________                                                 MgO                                                                    38      0            92        340   -405                                      39      1            71        632   -307                                      40      3            61        806   -210                                      41      10           43        941   -173                                       42*    20           27       1057    -67                                              CoO                                                                    32      0            92        340   -405                                      44      3            67        714   -258                                      45      5            75        555   -336                                      46      10           46       1518    -96                                       47*    20           32       4111    +32                                              ZnO                                                                    48      0            92        340   -405                                      49      1            76        539   -360                                      50      3            67        732   -276                                      51      5            57       1097   -100                                       52*    20           32       6355     20                                      ______________________________________                                    

In the tables, asterisked samples 27, 32, 37, 42, 47 and 52 are comparative examples beyond the scope of the present invention.

As can be seen from the tables 2 to 4, the Q value is improved by the addition of each of the additives. However, as the amount of the addition is increased, the Q value becomes larger, while the dielectric constant become lower. Consequently, the amount of the addition of each of the additives is suitably not more than 10 parts by weight per 100 parts by weight of (Li_(1/2) ·B³⁺ _(1/2)) TiO₃.

Description is now made of a third embodiment.

A microwave ceramic composition according to the third embodiment is obtained by selecting, in a composition formula of (A¹⁺ ·A^(1+'))₂ O-B³⁺ ₂ O₃ -TiO₂, Li¹⁺, Na¹⁺, and Nd³⁺ as A¹⁺, A^(1+'), and B³⁺, respectively. In the third embodiment, to prepare samples high-purity powders of TiO₂, Li₂ CO₃, Na₂ CO₃, and Nd₂ O₃ are used as raw materials, and the mixture ratio of the respective raw materials is changed in the same method as that in the first embodiment. The dielectric properties of the samples measured in the neighborhood of the measurement frequency of 3 GHz using the Hakki-Coleman method are shown in Table 5. In the table, w, x, y and z indicate molar fractions, where w+x+y+z=100 mole %.

                                      TABLE 5                                      __________________________________________________________________________          composition ratio (mole %)                                                sample                                                                              w.Li.sub.2 O--x.Na.sub.2 O--y.Nd.sub.2 O.sub.3 --z.TiO.sub.2                                     dielectric properties                                   number                                                                              w   x    y   z    ε                                                                          Q value                                                                             τ f(PPM/°C.)                        __________________________________________________________________________     53   1.00                                                                               8.33 18.13                                                                              72.54                                                                                76 805  +70                                            54   1.50                                                                               8.33 18.03                                                                              72.14                                                                                97 715  +57                                            55   2.00                                                                               8.33 17.93                                                                              71.74                                                                                96 665  +52                                            56   2.50                                                                               8.33 17.83                                                                              71.34                                                                               103 710  +41                                            57   3.00                                                                               8.33 17.73                                                                              70.94                                                                               104 720  +35                                            58   4.00                                                                               8.33 17.53                                                                              70.14                                                                               106 654  +21                                            59   4.36                                                                               4.55 18.22                                                                              72.87                                                                                98 810  -15                                            60   5.00                                                                               8.33 17.33                                                                              69.34                                                                               109 569   -2                                            61   5.82                                                                               4.55 17.93                                                                              71.70                                                                               101 740  -55                                            62   7.00                                                                               8.33 16.93                                                                              67.74                                                                               101 470  -80                                            63   7.27                                                                               4.55 17.64                                                                              70.54                                                                                96 665  -83                                            64   9.00                                                                               8.33 16.93                                                                              67.74                                                                               101 470  -80                                            65   10.18                                                                              4.55 17.05                                                                              68.22                                                                                91 555  -255                                           66   13.09                                                                              4.55 16.47                                                                              65.89                                                                                93 325  -165                                           __________________________________________________________________________

As can be seen from table 5, a dielectric ceramic composition expressed by a composition formula of w·Li₂ O-x·Na₂ O-y·Nd₂ O₃ -z·TiO₂ (w+x+y+z=100 mole %) has a high dielectric constant ε, has a low temperature coefficient of resonance frequency τf and has a high Q value.

    ______________________________________                                                0.0 mole % < w ≦ 17.0 mole %                                            0.0 mole % ≦ x ≦ 17.0 mole %                                     0.0 mole % < y ≦ 25.0 mole %                                            0.0 mole % < z ≦ 80.0 mole %                                     ______________________________________                                    

Particularly when w, x, y and z are set in the following ranges, good dielectric properties are obtained:

    ______________________________________                                                3.0 mole % ≦ w ≦ 15.0 mole %                                     3.0 mole % ≦ x ≦ 15.0 mole %                                     9.0 mole % ≦ y ≦ 25.0 mole %                                     0.0 mole % ≦ z ≦ 80.0 mole %                              ______________________________________                                    

Description is now made of a fifth embodiment.

A microwave ceramic composition according to the fifth embodiment is obtained by selecting, in a composition formula of (A¹⁺ ·A^(1+'))₂ O-B³⁺ ₂ O₃ -TiO₂, Li¹⁺, Na¹⁺, and Sm³⁺ as A¹⁺, A^(1+'), and B³⁺, respectively. In the fourth embodiment, high-purity powders of TiO₂, Li₂ CO₃, Na₂ CO₃, and Sm₂ O₃ are used as raw materials, and the mixture ratio of the respective raw materials is changed in the same method as that in the first embodiment, to prepare samples. The dielectric properties of the samples measured in the neighborhood of the measurement frequency of 3 GHz using the Hakki-Coleman method are shown in Table 6. In the table, w, x, y and z indicate molar fractions, where w+x+y+z=100 mole %.

                                      TABLE 6                                      __________________________________________________________________________     sample                                                                              composition ratio (mole %)                                                                       dielectric properties                                   number                                                                              w   x    y   z    ε                                                                          Q value                                                                             τ f(PPM/°C.)                        __________________________________________________________________________     w.Li.sub.2 O--x.Na.sub.2 O--y.Nd.sub.2 O.sub.3 --z.TiO.sub.2                   *67  0.00                                                                               16.67                                                                               16.67                                                                              66.66                                                                               73  2390 +213                                           68   3.00                                                                               6.68 18.67                                                                              71.66                                                                               80  1200 +51                                            69   3.60                                                                               6.68 17.96                                                                              71.76                                                                               80  1990 +41                                            70   3.75                                                                               6.68 17.17                                                                              72.41                                                                               83  2210 +44                                            71   4.50                                                                               6.68 18.67                                                                              70.16                                                                               80  2670   0                                            72   4.50                                                                               6.68 17.17                                                                              71.77                                                                               84  2100 +35                                            73   4.80                                                                               6.68 17.72                                                                              70.80                                                                               82  1870 +21                                            74   5.52                                                                               15.00                                                                               17.00                                                                              62.48                                                                               82  1790 +137                                           75   5.85                                                                               10.00                                                                               18.00                                                                              66.15                                                                               68  1610 +45                                            76   6.00                                                                               6.68 18.67                                                                              68.66                                                                               80  2530 -29                                            77   6.00                                                                               6.68 16.42                                                                              70.91                                                                               86  1590  +7                                            78   6.00                                                                               6.68 17.48                                                                              69.84                                                                               83  1975  +5                                            79   6.18                                                                               5.00 17.81                                                                              71.01                                                                               79  2750 -46                                            80   6.40                                                                               3.34 18.06                                                                              72.20                                                                               72  1180 -62                                            81   6.75                                                                               6.68 16.42                                                                              70.16                                                                               89  1180  -8                                            82   6.75                                                                               6.68 17.92                                                                              68.66                                                                               82  2140 -40                                            83   6.80                                                                               15.00                                                                               17.00                                                                              61.20                                                                               79  2270 +129                                           84   7.20                                                                               6.68 17.24                                                                              68.88                                                                               87  1430 -28                                            85   7.20                                                                               10.00                                                                               18.00                                                                              61.80                                                                               79  2140 +30                                            w.Li.sub.2 O--x.Na.sub.2 O--y.Nd.sub.2 O.sub.3 --z.TiO.sub.2                   86   7.76                                                                               3.00 19.40                                                                              69.84                                                                               71  1070 -119                                           87   8.00                                                                               3.34 16.33                                                                              72.33                                                                               74  2040  +8                                            88   8.00                                                                               3.34 17.74                                                                              70.92                                                                               72  2220 -91                                            89   8.00                                                                               3.34 19.33                                                                              69.33                                                                               71  2740 -122                                           90   8.10                                                                               10.00                                                                               17.10                                                                              64.80                                                                               85  1930 +44                                            91   8.75                                                                               3.00 18.74                                                                              69.74                                                                               72  2730 -132                                           92   9.00                                                                               3.34 18.33                                                                              69.33                                                                               70  2500 +138                                           93   10.80                                                                              6.68 16.52                                                                              66.00                                                                               102 1170 +55                                            94   12.00                                                                              6.68 16.28                                                                              65.04                                                                               82  1550 -20                                            95   14.40                                                                              3.34 16.46                                                                              65.80                                                                               68  1310 -184                                           __________________________________________________________________________

In the table, an esterified sample 67 is a comparative example beyond the scope of the present invention.

As can be seen from the table 6, a dielectric ceramic composition expressed by a composition formula of w·Li₂ O-x·Na₂ O-y·Sm₂ O₃ -z·TiO₂ (w+x+y+z=100 mole %) has a high dielectric constant ε, has a low temperature coefficient of resonance frequency τf and has a high Q value. In the sample 67 lacking Li₂ O, the absolute value of the temperature coefficient of resonance frequency τf is slightly high.

w, x, y and z are set in the following ranges:

    ______________________________________                                                0.0 mole % < w ≦ 17.0 mole %                                            0.0 mole % ≦ x ≦ 17.0 mole %                                     0.0 mole % < y ≦ 25.0 mole %                                            0.0 mole % < z ≦ 80.0 mole %                                     ______________________________________                                    

Particularly when w, x, y and z are set in the following ranges, good dielectric properties are obtained:

    ______________________________________                                                0.0 mole % < w ≦ 15.0 mole %                                            0.0 mole % ≦ x ≦ 15.0 mole %                                     0.0 mole % < y ≦ 20.0 mole %                                            0.0 mole % < z ≦ 75.0 mole %                                     ______________________________________                                    

Description is now made of a fifth embodiment.

A microwave ceramic composition according to the fifth embodiment is obtained by selecting, in a composition formula of (A¹⁺ ·A^(1+'))₂ O-(B³⁺ ·B^(3+'))₂ O₃ -TiO₂, Li¹⁺, Na¹⁺, Sm³⁺, and Nd³⁺ as A¹⁺, A^(1+'), B³⁺, and B^(3+'), respectively. In the fifth embodiment, high-purity powders of TiO₂, Li₂ CO₃, Na₂ CO₃, Nd₂ O₃, and Sm₂ O₃ are used as raw materials, and the mixture ratio of the respective raw materials is changed in the same method as that in the first embodiment, to prepare samples. The dielectric properties of the samples measured in the neighborhood of the measurement frequency of 3 GHz using the Hakki-Coleman method are shown in Table 7. In the table 7, v, w, x, y and z denote molar fractions, where v+w+x+y+z=100 mole %.

                                      TABLE 7                                      __________________________________________________________________________          composition ratio (mole %)                                                sample                                                                              v.Nd.sub.2 O.sub.3 --w.Li.sub.2 O--x.Na.sub.2 O--y.Sm.sub.2 O.sub.3            --z.TiO.sub.2          dielectric properties                              number                                                                              v    w   x    y   z    ε                                                                          Q value                                                                             τ f(PPM/°C.)                   __________________________________________________________________________      97  3.33 4.80                                                                               3.33 15.04                                                                              73.50                                                                               83   750 +24                                        98  3.33 5.20                                                                               3.33 15.60                                                                              72.54                                                                               81  1250  +3                                        99  3.33 6.40                                                                               3.33 14.72                                                                              72.22                                                                               79  2250 -71                                       100  3.33 8.00                                                                               3.33 14.40                                                                              70.94                                                                               77  2200 -99                                       101  3.33 11.20                                                                              3.33 13.76                                                                              68.38                                                                               67   790 -212                                      102  3.33 14.40                                                                              3.33 13.12                                                                              65.82                                                                               75   640 -186                                      103  6.66 3.90                                                                               6.66 11.7                                                                               71.08                                                                               89  1850  -1                                       104  6.66 3.60                                                                               6.66 11.28                                                                              71.80                                                                               92  1480 +22                                       105  6.66 4.80                                                                               6.66 11.04                                                                              70.84                                                                               78  2370 -69                                       106  6.66 6.00                                                                               6.66 10.80                                                                              69.88                                                                               94  1410 -10                                       107  6.66 8.40                                                                               6.66 10.32                                                                              67.96                                                                               98   860 -10                                       108  6.66 10.80                                                                              6.66 9.84                                                                               66.04                                                                               113  570 + 77                                      __________________________________________________________________________

As can be seen from the table 7, a dielectric ceramic composition expressed by a composition formula of v·Nd₂ O₃ -w·Li₂ O-x·Na₂ O-y·Sm₂ O₃ -x·TiO₂ (v+w+x+y+z=100 mole %) has a high dielectric constant ε, has a low temperature coefficient of resonance frequency τf and has a high Q value.

v, w, x, y and z are set in the following ranges:

    ______________________________________                                                0.0 mole % < v ≦ 25.0 mole %                                            0.0 mole % ≦ w ≦ 17.0 mole %                                     0.0 mole % < x ≦ 17.0 mole %                                            0.0 mole % < y ≦ 25.0 mole %                                            0.0 mole % < z ≦ 80.0 mole %                                     ______________________________________                                    

Particular when v, w, x, y and z are set in the following ranges, good dielectric properties are obtained:

    ______________________________________                                                3.0 mole % ≦ v ≦ 7.0 mole %                                      3.0 mole % ≦ w ≦ 15.0 mole %                                     0.0 mole % ≦ x ≦ 7.0 mole %                                      0.0 mole % < y ≦ 16.0 mole %                                            0.0 mole % < z ≦ 75.0 mole %                                     ______________________________________                                    

Description is now made of a sixth embodiment.

A microwave ceramic composition according to the sixth embodiment is obtained by selecting, in a composition formula of (A¹⁺ ·A^(1+'))₂ O-(B³⁺ ·B^(3+'))₂ O₃ -TiO₂, Li¹⁺, Na¹⁺, Sm³⁺, and Pr³⁺ as A¹⁺, A^(1+'), B³⁺, and B^(3+'), respectively. In the sixth embodiment, high-purity powders of TiO₂, Li₂ CO₃, Na₂ CO₃, Nd₂ O₃, and Pr₆ O₁₁ are used as raw materials, and the mixture ratio of the respective raw materials is changed in the same method as that in the first embodiment, to prepare samples. The dielectric properties of the samples measured in the neighborhood of the measurement frequency of 3 GHz using the Hakki-Coleman method are shown in Table 8. In the table, v, w, x, y and z indicate molar fractions, where v+w+x+y+z=100 mole %.

                                      TABLE 8                                      __________________________________________________________________________          composition ratio (mole %)                                                sample                                                                              v.Pr.sub.2 P.sub.3 --w.Li.sub.2 O--x.Na.sub.2 O--y.Sm.sub.2 O.sub.3            --z.TiO.sub.2          dielectric properties                              number                                                                              v    w   x    y   z    ε                                                                          Q value                                                                             τ f(PPM/°C.)                   __________________________________________________________________________     109  3.33 4.80                                                                               3.33 15.04                                                                              73.50                                                                               84  830  +26                                       110  3.33 6.40                                                                               3.33 14.72                                                                              72.22                                                                               81  2050 -50                                       111  3.33 8.00                                                                               3.33 14.40                                                                              70.94                                                                               78  2000 -97                                       112  3.33 11.20                                                                              3.33 13.76                                                                              68.38                                                                               69  720  -217                                      113  3.33 14.40                                                                              3.33 13.12                                                                              65.82                                                                               76  670  -195                                      114  6.66 3.60                                                                               6.66 11.28                                                                              71.80                                                                               95  1170 +34                                       115  6.66 4.80                                                                               6.66 11.04                                                                              70.84                                                                               95  1120 +15                                       116  6.66 6.00                                                                               6.66 10.80                                                                              69.88                                                                               99  1080 +16                                       117  6.66 8.40                                                                               6.66 10.32                                                                              67.96                                                                               106 560  +20                                       118  6.66 10.80                                                                              6.66 9.84                                                                               66.04                                                                               115 390  +93                                       __________________________________________________________________________

As can be seen from the table 8, a dielectric ceramic composition expressed by a composition formula of v·Pr₂ O₃ -w·Li₂ O-x·Na₂ O-y·Sm₂ O₃ -z·TiO₂ (v+w+x+y+z=100 mole %) has a high dielectric constant ε, has a low temperature coefficient of resonance frequency τf and has a high Q value.

v, w, x, y and z are set in the following ranges:

    ______________________________________                                                0.0 mole % < v ≦ 7.0 mole %                                             0.0 mole % < w ≦ 15.0 mole %                                            0.0 mole % ≦ x ≦ 7.0 mole %                                      0.0 mole % < y ≦ 16.0 mole %                                            0.0 mole % < z ≦ 75.0 mole %                                     ______________________________________                                    

Particularly when v, w, x, y and z are set in the following ranges, good dielectric properties are obtained:

    ______________________________________                                                 3.0 mole % ≦ v ≦ 7.0 mole %                                      3.0 mole % ≦ w ≦ 15.0 mole %                                     3.0 mole % ≦ x ≦ 7.0 mole %                                      9.0 mole % ≦ y ≦ 16.0 mole %                                    65.0 mole % ≦ z ≦ 75.0 mole %                             ______________________________________                                    

Description is now made of a seventh embodiment.

A microwave ceramic composition according to the seventh embodiment is obtained by selecting, in a composition formula of A¹⁺ ₂ O-CaO-B³⁺ ₂ O₃ -TiO₂, Li¹⁺ and Sm³⁺ as A¹⁺ and B³⁺, respectively. In the seventh embodiment, high-purity powders of TiO₂, Li₂ CO₃, CaCO₃, and Sm₂ O₃ are used as raw materials, and the mixture ratio of the respective raw materials is changed in the same method as that in the first embodiment, to prepare samples. The dielectric properties of the samples measured in the neighborhood of the measurement frequency of 3 GHz using the Hakki-Coleman method are shown in Table 9. In the table, w, x, y and z denote molar fractions, where v+w+x+y+z=100 mole %.

                                      TABLE 9                                      __________________________________________________________________________           composition ratio (mole %)                                               sample                                                                               w.Li.sub.2 O--x.CaO--y.Sm.sub.2 O.sub.3 --z.TiO.sub.2                                            dielectric properties                                  number                                                                               w   x    y   z    ε                                                                          Q value                                                                             τ f(PPM/°C.)                       __________________________________________________________________________     119   3.50                                                                               20.00                                                                               11.28                                                                              65.12                                                                               90  1840 +164                                          120   4.80                                                                               10.00                                                                               15.40                                                                              70.16                                                                               87  1590 +21                                           121   4.80                                                                               20.00                                                                               11.04                                                                              64.16                                                                               104 1720 +155                                          122   5.00                                                                               10.00                                                                               10.00                                                                              75.00                                                                               89  1390 +55                                           123   6.00                                                                               20.00                                                                               10.80                                                                              63.20                                                                               111 1630 +156                                          124   6.40                                                                               10.00                                                                               14.72                                                                              68.88                                                                               92  1910  +8                                           125   8.00                                                                               10.00                                                                               14.40                                                                              67.60                                                                               95  1780  -8                                           126   8.40                                                                               20.00                                                                               10.32                                                                              61.28                                                                               121 1510 +179                                          127   11.20                                                                              10.00                                                                               13.76                                                                              65.04                                                                               106 1550  +8                                           128   20.00                                                                              10.00                                                                               10.00                                                                              75.00                                                                               75  1700 -44                                           129   7.00                                                                               17.00                                                                               13.00                                                                              63.00                                                                               98  1980 -15                                           130   8.00                                                                               17.00                                                                               12.00                                                                              63.00                                                                               104 1500  +7                                           131   9.00                                                                               16.00                                                                               12.00                                                                              63.00                                                                               105 1550  -2                                           132   9.00                                                                               17.00                                                                               11.00                                                                              63.00                                                                               108 1190 +45                                           133   12.50                                                                              12.50                                                                               12.50                                                                              62.50                                                                               103 1277  +6                                           134   8.82                                                                               23.53                                                                               8.82                                                                               58.83                                                                               123 1156 +154                                          135   5.56                                                                               33.33                                                                               5.56                                                                               55.55                                                                               133 1025 +457                                          136   2.63                                                                               42.11                                                                               2.63                                                                               52.63                                                                               108 1190 +835                                          __________________________________________________________________________

As can be seen from the table 9, a dielectric ceramic composition expressed by a composition formula of w·Li₂ O-x·CaO-y·Sm₂ O₃ -z·TiO₂ (w+x+y+z=100 mole %) has a high dielectric constant ε, has a low temperature coefficient of resonance frequency τf and has a high Q value.

Particularly when v, w, x, y and z are set in the following ranges, good dielectric properties are obtained:

    ______________________________________                                                0.0 mole % < w ≦ 25.0 mole %                                            0.0 mole % ≦ x < 50.0 mole %                                            0.0 mole % < y ≦ 20.0 mole %                                            0.0 mole % < z ≦ 80.0 mole %                                     ______________________________________                                    

Description is now made of an eighth embodiment.

A microwave ceramic composition according to the eighth embodiment is obtained by selecting, in a composition formula of A¹⁺ ₂ O-CaO-B³⁺ ₂ O₃ -TiO₂, Li¹⁺ and Nd³⁺ as A¹⁺ and B³⁺, respectively. In the eighth embodiment, high-purity powders of TiO₂, Li₂ CO₃, CaCO₃, and Nd₂ O₃ are used as raw materials, and the mixture ratio of the respective raw materials is changed in the same method as that in the first embodiment, to prepare samples. The dielectric properties of the samples measured in the neighborhood of the measurement frequency of 3 GHz using the Hakki-Coleman method are shown in Table 10. In the table, w, x, y and z indicate molar fractions, where v+w+x+y+z=100 mole %.

                                      TABLE 10                                     __________________________________________________________________________           composition ratio (mole %)                                               sample                                                                               w.Li.sub.2 O--x.CaO--y.Nd.sub.2 O.sub.3 --z.TiO.sub.2                                            dielectric properties                                  number                                                                               w   x    y   z    ε                                                                          Q value                                                                             τ f(PPM/°C.)                       __________________________________________________________________________     137   14.52                                                                              6.45 14.52                                                                              64.52                                                                               104 810  -129                                          138   4.00                                                                               16.66                                                                               12.53                                                                              66.80                                                                               109 672   +8                                           139   5.00                                                                               16.66                                                                               12.27                                                                              65.73                                                                               114 790   +5                                           140   6.70                                                                               16.66                                                                               12.00                                                                              64.67                                                                               118 802   +3                                           141   9.30                                                                               16.66                                                                               11.47                                                                              62.53                                                                               118 820   +12                                          142   12.00                                                                              16.66                                                                               10.93                                                                              60.40                                                                               124 662   +18                                          143   18.00                                                                              16.66                                                                               8.74                                                                               56.60                                                                               141 405   +25                                          144   8.50                                                                               30.50                                                                               5.50                                                                               55.50                                                                               151 1785 +275                                          145   1.70                                                                               28.57                                                                               8.23                                                                               61.49                                                                               109 1265 +185                                          146   2.14                                                                               28.57                                                                               8.57                                                                               60.71                                                                               110 1500 +157                                          147   3.43                                                                               28.57                                                                               7.89                                                                               60.11                                                                               124 834  +128                                          148   6.00                                                                               28.57                                                                               7.37                                                                               58.06                                                                               129 1105 +131                                          149   12.50                                                                              12.50                                                                               12.50                                                                              62.50                                                                               125 879   +38                                          150   8.82                                                                               23.53                                                                               8.82                                                                               58.83                                                                               135 989  +171                                          151   5.56                                                                               33.33                                                                               5.56                                                                               55.55                                                                               141 962  +323                                          152   2.63                                                                               42.11                                                                               2.63                                                                               52.63                                                                               150 1683 +472                                          __________________________________________________________________________

As can be seen from the table 10, a dielectric ceramic composition expressed by a composition formula of w·Li₂ O-x·CaO-y·Nd₂ O₃ -z·TiO₂ (w+x+y+=100 mole %) has a high dielectric constant ε, has a low temperature coefficient of resonance frequency τf and has a high Q value.

w, x, y and z set in the following ranges:

    ______________________________________                                                0.0 mole % < w ≦ 25.0 mole %                                            0.0 mole % ≦ x < 50.0 mole %                                            0.0 mole % < y ≦ 20.0 mole %                                            0.0 mole % < z ≦ 80.0 mole %                                     ______________________________________                                    

Particularly when w, x, y and z are set in the following ranges, good dielectric properties are obtained;

    ______________________________________                                                 0.0 mole % < w ≦ 20.0 mole %                                            0.0 mole % ≦ x < 50.0 mole %                                            0.0 mole % < y ≦ 20.0 mole %                                           50.0 mole % ≦ z ≦ 80.0 mole %                             ______________________________________                                    

Description is now made of a ninth embodiment. A ceramic composition according to the ninth embodiment is obtained by mixing the ceramic composition (Li_(1/2) ·B³⁺ _(1/2)) TiO₃ obtained in the above described first embodiment and a ceramic composition (Na_(1/2) ·C³⁺ _(1/2))TiO₃ having dielectric constant ε and having a temperature coefficient of resonance frequency τf which is large on the plus side. At this time, Nd³⁺ or Sm³⁺ and Nd³⁺ or Sm³⁺ are respectively selected as B³⁺ and C³⁺.

Samples are prepared in the same method as that in the first embodiment, and the dielectric constant ε, the Q value, and the temperature coefficient of resonance frequency τf of the samples are measured in the neighborhood of the measurement frequency of 3 GHz using the Hakki-Coleman method.

The results of the measurements are shown in Table 11 and Table 12. In the tables, a, b, c and d are as follows:

    ______________________________________                                         a: (Li.sub.1/2.Nd.sub.1/2) TiO.sub.3                                                               b: (Na.sub.1/2.Nd.sub.1/2) TiO.sub.3                       c: (Li.sub.1/2.Sm.sub.1/2) TiO.sub.3                                                               d: (Na.sub.1/2.Sm.sub.1/2) TiO.sub.3                       ______________________________________                                    

                  TABLE 11                                                         ______________________________________                                                      dielectric properties                                             sample mixture ratio                                                                              dielectric Q     τ f                                    number (mole %)    constant ε                                                                        value (PPM/°C.)                           ______________________________________                                                a       b                                                               153    80      20      100      851   -15                                      154    60      40      108      511    58                                      155    40      60      106      513   205                                      156    20      80       88      881   245                                             a       d                                                               157    80      20       95      1099  -7                                       158    60      40       99      914    32                                      159    40      60       95      1072  144                                      160    20      80       75      1566  185                                      ______________________________________                                    

                  TABLE 12                                                         ______________________________________                                                      dielectric properties                                             sample mixture ratio                                                                              dielectric Q     τ f                                    number (mole %)    constant ε                                                                        value (PPM/°C.)                           ______________________________________                                                c       b                                                               161    80      20      76       1665  -64                                      162    60      40      89       1297   12                                      163    40      60      99        910  162                                      164    20      80      90       1081  220                                             c       d                                                               165    80      20      70       1884  -69                                      166    60      40      79       2023   17                                      167    40      60      81       1314  116                                      168    20      80      68       1537  178                                      ______________________________________                                    

As can be seen from the tables 11 and 12, a ceramic composition having a high dielectric constant ε, having a low temperature coefficient of resonance frequency τf and having a high Q value is obtained by mixing a ceramic composition (Na_(1/2) ·C³⁺ _(1/2)) TiO₃ (C³⁺ : Nd³⁺, Sm³⁺) having a high dielectric constant ε and having a temperature coefficient of resonance frequency τf which is large on the plus side and a ceramic composition (Li_(1/2) ·B³⁺ _(1/2)) TiO₃ (B³⁺ : Nd³⁺, Sm³⁺) having a high dielectric constant ε and having a temperature coefficient of resonance frequency τf which is large on the minus side.

FIG. 1 is a characteristic diagram showing the characteristic curve of a dielectric constant ε and a temperature coefficient of resonance frequency τf against the mixture ratio of (Li_(1/2) ·Sm_(1/2)) TiO₃ to (Na_(1/2) ·Sm_(1/2)) TiO₃. The mixture ratio is thus changed, to obtain ceramic compositions having various properties.

The ceramic composition according to the ninth embodiment shown in the tables 11 and 12 is obtained by mixing the ceramic composition (Li_(1/2) ·Nd_(1/2)) TiO₃ or (Li_(1/2) ·Sm_(1/2)) TiO₃ obtained in the above described first embodiment and a ceramic composition (Na_(1/2) ·Nd_(1/2)) TiO₃ or (Na_(1/2) ·Sm_(1/2)) TiO₃ having a high dielectric constant ε and having a temperature coefficient of resonance frequency τf which is large on the plus side. When the same ceramic composition as that in the ninth embodiment is obtained using high-purity powders of TiO₂, Li₂ CO₃, Na₂ CO₃, Sm₂ O₃, and Nd₂ O₃ as raw materials, the mixture ratios of the respective raw materials are as shown in Table 13 to Table 15. The dielectric properties of samples of the ceramic composition formed in the mixture ratios are the same as those of the samples shown in the tables 11 and 12. In the tables 13 to 15, sample numbers in parentheses correspond to the samples shown in the tables 11 and 12.

                  TABLE 13                                                         ______________________________________                                                   composition ratio (mole %)                                           sample    w.Li.sub.2 O--x.Na.sub.2 O--y.Nd.sub.2 O.sub.3 --z.TiO.sub.2         number    w        x         y      z                                          ______________________________________                                         169(153)  13.33    3.33      16.67  66.67                                      170(154)  9.99     6.77      16.67  66.67                                      171(155)  6.77     9.99      16.67  66.67                                      172(156)  3.33     13.33     16.67  66.67                                      ______________________________________                                    

                  TABLE 14                                                         ______________________________________                                                composition ratio (mole %)                                              sample v.Nd.sub.2 O.sub.3 --w.Li.sub.2 O--x.Na.sub.2 O--y.Sm.sub.2                    O.sub.3 --z.TiO.sub.2                                                   number v         w       x       y     z                                       ______________________________________                                         173(157)                                                                              13.34     13.33   3.33    3.33  66.67                                   174(158)                                                                              9.99      9.99    6.67    6.68  66.67                                   175(159)                                                                              6.68      6.67    9.99    9.99  66.67                                   176(160)                                                                              3.34      3.33    13.33   13.33 66.67                                   177(161)                                                                              3.33      13.33   3.33    13.34 66.67                                   178(162)                                                                              6.68      9.99    6.67    9.99  66.67                                   179(163)                                                                              9.99      6.67    9.99    6.68  66.67                                   180(164)                                                                              13.33     3.33    13.33   3.34  66.67                                   ______________________________________                                    

                  TABLE 15                                                         ______________________________________                                                   composition ratio (mole %)                                           sample    w.Li.sub.2 O--x.Na.sub.2 O--y.Sm.sub.2 O.sub.3 --z.TiO.sub.2         number    w        x         y      z                                          ______________________________________                                         181(165)  13.33    3.33      16.67  66.67                                      182(166)  9.99     6.67      16.67  66.67                                      183(167)  6.67     9.99      16.67  66.67                                      184(168)  3.33     13.33     16.67  66.67                                      ______________________________________                                    

Description is now made of a tenth embodiment using CaTiO₃ as a ceramic composition having a high dielectric constant ε and having a temperature coefficient of resonance frequency τf which is large on the plus side.

Table 16 shows the results of measurements made of the dielectric properties of samples of a dielectric composition obtained by selecting, in a composition formula of (Li_(1/2) ·B³⁺ _(1/2)) TiO₃ -CaTiO₃, Nd³⁺ or Sm³⁺ as B³⁺ in the same manner as that in the first embodiment in the neighborhood of the measurement frequency of 3 GHz using the Hakki-Coleman method.

In the table 16, a and c are the same as those in the tables 11 and 12.

                  TABLE 16                                                         ______________________________________                                         sample                dielectric properties                                    num-  mixture ratio (mole %)                                                                         dielectric                                                                              Q     τ f                                   ber             CaTiO.sub.3                                                                              constant ε                                                                    value (PPM/°C.)                        ______________________________________                                               a                                                                        185   80        20        125     879   38                                     186   60        40        135     989  171                                     187   40        60        141     962  323                                     188   20        80        150    1683  472                                           c                                                                        189   80        20        103    1277   6                                      191   60        40        123    1156  154                                     192   40        60        133    1025  305                                     193   20        80        144    1822  457                                     ______________________________________                                    

As can be seen from the table 16, a dielectric ceramic composition having a dielectric constant ε which takes a large value exceeding 100 , having a low temperature coefficient of resonance frequency τf and having a high value is obtained.

A characteristic curve of a dielectric constant ε and a temperature coefficient of resonance frequency τf against the mixture ratio of (Li_(1/2) ·B³⁺ _(1/2)) TiO₃ to CaTiO₃ is shown in FIG. 2 (B³⁺ =Nd³⁺) and FIG. 3 (B³⁺ =Sm³⁺).

Description is now made of the tenth embodiment using CaTiO₃ as a ceramic composition having a high dielectric constant ε and having a temperature coefficient of resonance frequency τf which is large on the plus side.

The ceramic composition according to the tenth embodiment shown in the table 16 is obtained by mixing the ceramic composition (Li_(1/2) ·Nd_(1/2)) TiO₃ or (Li_(1/2) ·Sm_(1/2)) TiO₃ obtained in the above described first embodiment and CaTiO₃. When the same ceramic composition as that in the tenth embodiment is obtained using high-purity powders of TiO₂, Li₂ CO₃, Sm₂ O₃, Nd₂ O₃, and CaCO₃ as raw materials, the mixture ratios of the ceramic composition are as shown in Table 17 and Table 18. The dielectric properties of samples of a ceramic composition formed in the mixture ratios are the same as those of the samples shown in the table 16. In the tables 17 and 18, sample numbers in parentheses correspond to the samples shown in the table 16.

                  TABLE 17                                                         ______________________________________                                                    composition ratio (mole %)                                          sample     w.Li.sub.2 O--x.CaO--y.Nd.sub.2 O.sub.3 --z.TiO.sub.2               number     w       x          y     z                                          ______________________________________                                         194(185)   12.50   12.50      12.50 62.50                                      195(186)   8.82    23.53      8.82  58.83                                      196(187)   5.56    33.33      5.56  55.55                                      197(188)   2.63    42.11      2.63  52.63                                      ______________________________________                                    

                  TABLE 18                                                         ______________________________________                                                    composition ratio (mole %)                                          sample     w.Li.sub.2 O--x.CaO--y.Sm.sub.2 O.sub.3 --z.TiO.sub.2               number     w       x          y     z                                          ______________________________________                                         199(189)   12.50   12.50      12.50 62.50                                      199(190)   8.82    23.53      8.82  58.83                                      200(191)   5.56    33.33      5.56  55.55                                      201(192)   2.63    42.11      2.63  52.63                                      ______________________________________                                    

Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims. 

What is claimed is:
 1. A microwave dielectric ceramic composition comprising a composition according to the formula (A¹⁺ _(1/2) ·B³⁺ _(1/2))TiO₃, wherein A¹⁺ is Li¹⁺, and B³⁺ is a member of the group consisting of Nd⁺, Sm³⁺, Co³⁺ and Pr³⁺.
 2. A microwave dielectric ceramic composition consisting essentially of: 100 parts by weight of a ceramic (Li_(1/2) ·Nd_(1/2))TiO₃ ; and 10 parts by weight of a member from the group consisting of MgO, CoO, and ZnO.
 3. A microwave dielectric ceramic composition consisting essentially of: 100 parts by weight of a ceramic (Li_(1/2) ·Pr_(1/2))TiO₃ ; and 10 parts by weight of a member from the group consisting of MgO, CoO, and ZnO.
 4. A microwave dielectric ceramic composition consisting essentially of: 100 parts by weight of a ceramic (Li_(1/2) ·Sm_(1/2))TiO₃ ; and 10 parts by weight of a member from the group consisting of CaCO₃, SrCO₃, and ZnO.
 5. A microwave dielectric ceramic composition comprising a composition according to the formula w·A¹⁺ ₂ O-x·A^(1+') ₂ O-y·B³⁺ ₂ O₃ -z·TiO₂, wherein w+x+y+z=100 % mole, A¹⁺ is Li¹⁺, A^(1+'), is Na¹⁺, and B³⁺ is a member of the group consisting of Nd³⁺ or Sm³⁺.
 6. The microwave dielectric ceramic composition according to claim 2, wherein B³⁺ is Nd³⁺, and w, x, y and z are in the following ranges:

    ______________________________________                                                0.0 mole < w ≦ 17.0 mole %,                                             0.0 mole ≦ x ≦ 17.0 mole %,                                      0.0 mole < y ≦ 25.0 mole %,                                             0.0 mole < z ≦ 80.0 mole %.                                      ______________________________________                                    


7. The microwave dielectric ceramic composition according to claim 2, wherein B³⁺ is Sm⁺, and w, x, y and z are in the following ranges:

    ______________________________________                                                0.0 mole < w ≦ 17.0 mole %,                                             0.0 mole ≦ x ≦ 17.0 mole %,                                      0.0 mole < y ≦ 20.0 mole %,                                             0.0 mole < z ≦ 75.0 mole %.                                      ______________________________________                                    


8. A microwave dielectric ceramic composition comprising a composition according to the formula v·B^(3+') ₂ O₃ -w·A¹⁺ ₂ O-x·A^(1+') ₂ O-y·B³⁺ ₂ O₃ -z·TiO₂, wherein, A¹⁺ is Li¹⁺, A^(1+') is Na¹⁺, B³⁺ is Sm³⁺, and B^(3+') is a member of the group consisting of Nd³⁺ and Pr³⁺.
 9. The microwave dielectric ceramic composition according to claim 5, wherein B^(3+') is Nd⁺ and v, w, x, y and z are in the following ranges:

    ______________________________________                                                0.0 mole < v ≦ 25.0 mole %,                                             0.0 mole < w ≦ 17.0 mole %,                                             0.0 mole ≦ x ≦ 17.0 mole %,                                      0.0 mole < y ≦ 25.0 mole %,                                             0.0 mole < z ≦ 80.0 mole %.                                      ______________________________________                                    


10. The microwave dielectric ceramic composition according to claim 5, wherein B^(3+') is Pr³⁺, and v, w, x y and z are in the following ranges:

    ______________________________________                                                0.0 mole < v ≦ 7.0 mole %,                                              0.0 mole < w ≦ 15.0 mole %,                                             0.0 mole ≦ x ≦ 7.0 mole %,                                       0.0 mole < y ≦ 16.0 mole %,                                             0.0 mole < z ≦ 75.0 mole %.                                      ______________________________________                                    


11. A microwave dielectric ceramic composition comprising a composition according to the formula w·A¹⁺ ₂ O-x·CaO-y·B³⁺ O₃ -z·TiO₂, wherein w+x+y+z=100 % mole, A¹⁺ is Li¹⁺, and B³⁺ is a member of the group consisting of Sm³⁺ an Nd³⁺.
 12. The microwave dielectric ceramic composition according to claim 8, wherein B³⁺ is Sm³⁺, and w, x, y and z are in the following ranges:
 13. The microwave dielectric ceramic composition according to claim 8, wherein B³⁺ is Nd³⁺, and w, x, y and z are in the following ranges:

    ______________________________________                                                0.0 mole < w ≦ 25.0 mole %,                                             0.0 mole ≦ x < 50.0 mole %,                                             0.0 mole < y ≦ 20.0 mole %,                                             0.0 mole < z ≦ 80.0 mole %.                                      ______________________________________                                    

    ______________________________________                                                0.0 mole < w ≦ 25.0 mole %,                                             0.0 mole ≦ x < 50.0 mole %,                                             0.0 mole < y ≦ 20.0 mole %,                                             0.0 mole < z ≦ 80.0 mole %.                                      ______________________________________                                    


14. A microwave dielectric ceramic composition comprising a composition according to the formula x·(Li_(1/2) ·B³⁺ _(1/2)) TiO₃ -(100-x) (Na_(1/2) ·C³⁺ _(1/2)) TiO₃, wherein 0 mole %<x<100 mole %, and B⁺ and C³⁺ are, respectively, a member of the group consisting of Nd³⁺ and Sm³⁺.
 15. A microwave dielectric ceramic composition comprising a composition according to the formula x·(Li_(1/2) ·B³⁺ _(1/2)) TiO₃ -(100-x) (CaTiO₃, wherein 0 mole %<x<100 mole %, and B³⁺ is a member of the group consisting of Nd³⁺ and Sm³⁺. 